software quality assurance

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Software Quality Assurance - Outline : 

November 15, 1997 2 Software Quality Assurance - Outline What is Software Quality assurance(SQA)? Quality Concepts. Software Quality Assurance Activities. Software Reviews and their importance Statistical SQA. Software Reliability ISO 9000 approach to SQA

What is SQA? : 

November 15, 1997 3 What is SQA? Software Quality Assurance is an umbrella activity that is applied throughout the software process...

It encompasses.. : 

November 15, 1997 4 It encompasses.. A quality management approach Effective software engineering technology Formal technical reviews that are applied throughout the software process A multitiered testing strategy Control of software documentation and changes to it A procedure to assure compliance with software development standards Measurement and reporting techniques

Quality ??? : 

November 15, 1997 5 Quality ??? Quality refers to any measurable characteristics such as correctness, maintainability, portability, testability, usability, reliability, efficiency, integrity, reusability and interoperability.

Quality Concepts : 

November 15, 1997 6 Quality Concepts Quality of Design refers to the characteristics that designer’s specify for an item. Quality Control is the series of inspections, reviews and tests used throughout the development cycle to ensure that each work product meets the requirements placed upon it. Quality of Conformance is the degree to which the design specifications are followed during manufacturing.

(cont'd)... : 

November 15, 1997 7 (cont'd)... Quality policy refers to the basic aims and objectives of an organization regarding quality as stipulated by the management. Quality assurance consists of the auditing and reporting functions of management. Cost of Quality includes all costs incurred in the pursuit of quality or in performing quality related activities such as appraisal costs, failure costs and external failure costs.

(cont'd)... : 

November 15, 1997 8 (cont'd)... Quality planning is the process of assessing the requirements of the procedure and of the product and the context in which these must be observed. Quality testing is assessment of the extent to which a test object meets given requirements Quality assurance plan is the central aid for planning and checking the quality assurance. Quality assurance system is the organizational structure, responsibilities, procedures, processes and resources for implementing quality management.

Relative cost of correcting an error : 

November 15, 1997 9 Relative cost of correcting an error

Defn. of Software Quality Assurance : 

November 15, 1997 10 Defn. of Software Quality Assurance Conformance to explicitly stated functional and performance requirements, explicitly documented development standards, and implicit characteristics that are expected of all professionally developed software.

SQA Group Plan : 

November 15, 1997 11 SQA Group Plan Evaluations to be performed Audits and reviews to be performed Standards that are applicable to the project Procedures for error reporting and tracking Documents to be produced by the SQA group Amount of feedback provided to software project team

SQA Group Activities : 

November 15, 1997 12 SQA Group Activities Participates in the development of the projects software process description Reviews software engineering activities to verify compliance with the defined software process. Audits designated software work products to verify compliance with those defined as part of the software process.

(cont'd)... : 

November 15, 1997 13 (cont'd)... Ensures that deviations in software work and work products are documented and handled according to a document procedure. Records any non-compliance and reports to senior management.

Software Reviews : 

November 15, 1997 14 Software Reviews ‘Filter’ for the software engineering process ‘Purify’ the software work products that occur as a result of analysis, design, and coding. Achieve technical work of more uniform, greater and more predictable quality. Detect errors and problems at the earliest possible time.

Formal Technical Reviews : 

November 15, 1997 15 Formal Technical Reviews To uncover errors in function, logic, or implementation for any representation of the software To verify that software meets its requirements To ensure that software representation meets predefined standards To achieve software development in a uniform manner To make projects more manageable

Defect Amplification Model : 

November 15, 1997 Defect Amplification Model

Defect Amplification with Reviews : 

November 15, 1997 Defect Amplification with Reviews

Cost Comparison of Error Repair : 

November 15, 1997 Cost Comparison of Error Repair

Review Guidelines.. : 

November 15, 1997 16 Review Guidelines.. Review the product, not producer Set an agenda and maintain it Limit the debate Enunciate problem areas, not to solve every problem noted Take written notes Allocate resources and time schedule for FTR’s Limit the number of participants and insist upon advance preparation Develop a checklist for each work product to be reviewed Training for all reviewer’s Reviewing earlier reviews

Additional Structures : 

November 15, 1997 Additional Structures Requirements Control Board All requirement changes must be formally reviewed and approved Software Control Board All design changes must be formally reviewed and approved Interface Control Board

Statistical Quality Assurance : 

November 15, 1997 17 Statistical Quality Assurance Implies information about software defects is collected and categorized An attempt is made to trace each defect to its underlying cause Isolate the vital few causes of the major source of all errors Then move to correct the problems that have caused the defects

Categories of Errors : 

November 15, 1997 Categories of Errors Incomplete or erroneous specification (IES) Misinterpretation of customer comm (MCC) Intentional deviation from specification (IDS) Violation of programming standards (VPS) Error in data representation (EDR) Inconsistent module interface (IMI) Error in design logic (EDL)

Categories of Errors (cont'd) : 

November 15, 1997 Categories of Errors (cont'd) Incomplete or erroneous testing (IET) Inaccurate or incomplete documentation (IID) Error in programming lang. Translation (PLT) Ambiguous or inconsistent human-computer interface (HCI) Miscellaneous (MIS) Most often IES, MCC and EDR are the vital few causes for majority of errors.

Definitions : 

November 15, 1997 18 Definitions Ei = the total number of errors uncovered during the ith step in the software engineering process Si = the number of serious errors Mi = the number of moderate errors Ti = the number of minor errors PS = size of the product (LOC, design statements, pages of documentation)

error index : 

November 15, 1997 19 error index Phase index for each step and then error index is calculated PIi = ws(Si/Ei)+wm(Mi/Ei)+wt(Ti/Ei) Formula:

Software Reliability : 

November 15, 1997 20 Software Reliability Defined as the probability of failure free operation of a computer program in a specified environment for a specified time. It can measured, directed and estimated A measure of software reliability is mean time between failures where MTBF = MTTF + MTTR MTTF = mean time to failure MTTR = mean time to repair

Software Availability : 

November 15, 1997 21 Software Availability Availability =MTTF/(MTTF + MTTR) * 100% Software availability is the probability that a program is operating according to requirements at a given point in time

Software Safety : 

November 15, 1997 Software Safety Processes that help reduce the probability that critical failures will occur due to SW Hazard analyses Identify hazards that could call failure Develop fault tree Identify all possible causes of the hazard Formally review the remedy for each Redundancy Require a written software safety plan Require independent verification & validation

Example Fault Tree -- Thermal : 

November 15, 1997 Example Fault Tree -- Thermal Loss of heat Power failure Computer failure Incorrect input SW failed to throw switch ... Computer failure SW failed to throw switch ... Logic reversed

Software Safety : 

November 15, 1997 Software Safety Redundancy Replicated at the hardware level Similar vs.. dis-similar redundancy Verification Assuring that the software specifications are met Validation Assuring that the product functions as desired Independence

Overview of SQA Plan : 

November 15, 1997 22 Overview of SQA Plan Purpose of Plan References Management Documentation Standards, Practices and Conventions Reviews and Audits Test Problem Reporting and Corrective action Tools, Techniques and Methodologies Code Control Media Control Supplier control Records Collection, Maintenance and Retention Training Risk Management

ISO 9000 Quality Standards : 

November 15, 1997 23 ISO 9000 Quality Standards ISO 9000 describes quality assurance elements in generic terms that can be applied to any business. It treats an enterprise as a network of interconnected processes. To be ISO-complaint processes should adhere to the standards described. Elements include organizational structure, procedures, processes and resources. Ensures quality planning, quality control, quality assurance and quality improvement.

ISO 9001 : 

November 15, 1997 24 ISO 9001 An international standard which provides broad guidance to software developers on how to Implement, maintain and improve a quality software system capable of ensuring high quality software Consists of 20 requirements... Differs from country to country..

ISO 9001 (cont'd)..requirements : 

November 15, 1997 25 ISO 9001 (cont'd)..requirements Management responsibility Quality system Contract review Design Control Document and data control Purchasing Control of customer supplied product Product identification and traceability Process control Inspection and testing Control of inspection, measuring and test equipment

ISO 9001 (cont'd).. : 

November 15, 1997 26 ISO 9001 (cont'd).. Inspection and test status Control of non-confirming product Corrective and preventive action Handling, storage, packaging, preservation and delivery Control of quality records Internal quality audits Training Servicing Statistical techniques

Summary- : 

November 15, 1997 27 Summary- SQA must be applied at each step SQA might be complex Software reviews are important SQA activities Statistical SQA helps improve product quality and software process Software Safety is essential for critical systems ISO 9001 standardizes the SQA activities